Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Semiconductor devices perform a wide range of functions such as analog and digital signal processing, sensors, transmitting and receiving electromagnetic signals, controlling electronic devices, power management, and audio/video signal processing. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, diodes, rectifiers, thyristors, and power metal-oxide-semiconductor field-effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, application specific integrated circuits (ASIC), power conversion, standard logic, amplifiers, clock management, memory, interface circuits, and other signal processing circuits.
A need exists in the semiconductor industry for smaller and thinner package size so that the end products, such as cell phones, computers, and watches, can be reduced in size and weight. Semiconductor die typically mounted to a leadframe or substrate, such as shown in FIG. 1. Semiconductor die 50 has an active surface 52 and back surface 54. A metal layer 56 is formed over back surface 54. Semiconductor die 50 is mounted metal layer 56 to leadframe 60 with a solder fillet or conductive epoxy 62. The solder fillet or conductive epoxy 62 typically flows up side surfaces 58 of semiconductor die 50 to form a good bond. As semiconductor die 50 become thinner and smaller, solder fillet or conductive epoxy 62 may wick-up side surfaces 58 too far and possibly migrate onto active surface 52. Solder fillet or conductive epoxy 62 on active surface 52 can create manufacturing issues, such as short circuits and leakage.
The potential for wicking solder fillet or conductive epoxy 62 too far on side surfaces 58 and onto active surface 52 limits how thin semiconductor die 50 can be made and still avoid such conditions. The thinner semiconductor die 50 is more susceptible since the active area is closer to the wicking of the solder fillet or conductive epoxy 62. On the other hand, making solder fillet or conductive epoxy 62 thinner to accommodate the thinner semiconductor die 50 reduces the strength of the interconnect. In addition, the smaller semiconductor die is more difficult to handle and therefore are more susceptible to rotating off of the horizontal access and bringing the solder or epoxy closer to active surface 52.
In FIG. 2, flipchip semiconductor die 70 has an active surface 72 with interconnect pads 74 and back surface 76. Semiconductor die 70 is positioned over substrate 80 with interconnect pads 74 oriented toward the substrate. A solder 82 is formed between interconnect pads 74 and conductive traces 84 on substrate 80 to provide electrical interconnect. Solder fillet 82 may wick-up side surfaces 86 of semiconductor die 70 and encroach on active surface 72. Solder fillet 82 wicking too far on side surfaces 76 or onto active surface 72 can create manufacturing issues, such as short circuits and leakage.